<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="UTF-8">
        <title>Title</title>
        <link rel="stylesheet" href="css/bcp.css" media="screen and (max-width:630px)">
        <link rel="stylesheet" href="css/bcb.css" media="screen and (min-width:640px)and (max-width:960px)">
        <link rel="stylesheet" href="css/bcy.css" media="screen and (min-width:960px)">
    </head>
    <body>
        <div class="box"></div>
    </body>
</html>